The present invention pertains to a measuring device. More particularly the present invention pertains to a device for measuring a distance on a graph, chart, map, or similar paper to enable rapid determination of a value represented by an indication on the paper.
Many procedures involve the determination of a value represented by an indication on a chart, graph, map, or other such paper. The magnitude of this value is dependent, in part, on the scale or calibration of the paper. By way of illustration, in a number of medical procedures a graph or similar representation of a physical phenomenon is obtained and must be analyzed to enable evaluation of a patient's condition. A typical example is the reading of an echocardiogram, the tracing of waveforms resulting from bouncing sound waves off the heart. Electrical signals resulting from the sound waves are applied to a cathode ray tube display device, and an appropriate display is generated. The scale, calibration, or magnification of the display may be varied by means of controls on the cathode ray tube display device until a suitable display is obtained. Calibration scale markings may be displayed on the screen in addition to the echocardiogram display. When the display on the screen is satisfactory, a hard copy of it can be obtained, for example by photographing the screen or by use of a recorder in conjunction with the cathode ray tube display device. The values of various points on the echocardiogram display can then be determined by comparison with the calibration scale indication. Since the final adjustment of the magnification of the echocardiogram is seldom the same for any two displays, this determination requires individual measurement of the calibration scale and of the echocardiogram and then calculation of the values represented by the echocardiogram.
As a second example, in many engineering operations blueprints must be read. Often a distance must be determined by measurements on the blueprints. The distance then depends upon the scale of the blueprint. Accordingly, to determine the distance, both the scale calibration of the blueprint and the measured distance must be known.
Similarly, determining a distance on a road map requires knowing both the calibration value for the road map and the measured distance on the road map so as to determine the measured value or the actual distance.
Various devices have been developed in the past for determination of a value on a chart, graph, map, or other such paper having a scale which might vary from one such paper to another. U.S. Pat. No. 2,296,104 shows a device for reading distances on such a paper. The device is placed over the paper, and racks on the device are extended to move pointers over the distance to be measured. The measurement is then indicated on mechanical dials. These dials can be changed by removing one set and installing a second set to change the scale of the device. This patent also shows a variation of the device in the form of a retractable tape measure having the readout dial attached to one face of the casing within which the tape retracts.
U.S. Pat. No. 3,973,326 shows a device for measuring distances on graphs, charts, maps, and the like. The paper on which the measurement is to be made is placed upon a table with one end of the distance to be measured adjacent one arm of a T-square. The distance is then measured by movement of a cursor on the other arm of the T-square. The cursor is connected in an electrical circuit, the resistance of which is dependent upon the cursor position. The output of this circuit is applied to a digital voltmeter which thus provides a reading indicative of the measured distance. No means is shown for changing the scale of the measurement.
U.S. Pat. No. 3,058,225 shows an instrument for determining the depth of a recess within a tooth or other body. A probe is retractable within a sleeve. The end of the sleeve is positioned adjacent the recess to be measured, and the probe is then extended. Circuitry within the device provides an indication on a meter of the extent to which the probe has been extended. No scale changing technique is shown.
U.S. Pat. Nos. 3,024,396 and 3,987,552 show measuring devices in which a position is indicated by the resistance of a variable resistor incorporated into the device. U.S. Pat. Nos. 2,875,524, 3,276,131, 3,942,895, and 4,035,922 show other forms of measuring devices in which a position is indicated by the magnitude of an electrical characteristic in a circuit. U.S. Pat. No. 2,886,892 shows an electrical caliper device in which a distance is measured and the measurement of that actual distance is indicated on a scale in accordance with the resistance of a rheostat controlled by the measuring calipers.
None of these prior art devices, however, permits rapid and accurate determination of a value represented by an indication on a chart, graph, map, or other such paper on which the scale may vary. Thus, while various ones of these prior art devices may permit determination of an actual distance measured on a paper, and others of the devices may permit determination of a value represented by an indication on such a paper, none is suitable for use in applications for which the scale of the paper may vary, such as in the reading of echocardiograms, blueprints, or maps. While U.S. Pat. No. 2,296,104 does show a device for reading values represented by indications on a chart, graph, map, or the like, with various scales being accommodated, still that device is unsuitable for many such applications, including the reading of echocardiograms. To change the scale of that device, the dials on the device must be removed and replaced. This is a cumbersome and time consuming operation, and requires the keeping of numerous sets of dials. Even then, only a limited number of scales can be accommodated, and in many applications, for example the reading of echocardiograms, it is desirable to have a device having an infinitely variable scale.
U.S. patent application Ser. No. 908,440, now abandoned, (Attorney's Docket No. 80412), filed of even data herewith by Steven B. Heymsfield, discloses a measuring device for measuring the value represented by an indication on a graph, chart, map, or the like, having a scale and in which the measuring device can accommodate any calibration scale over a wide range. The measuring device of that patent application includes a first member, with a first reference indication on it, and a second member, with a second reference indication on it. The second member is movable with respect to the first member between a closed position, in which the two reference indications are adjacent each other, and an extended position, in which the two reference indications are separated. The first and second members are coupled to a microprocessor having a keyboard. The microprocessor is programmed to be responsive to a first actuation of the keyboard to determine a calibration value, indicative of the extent to which the first and second reference indications are separated at the time of that first actuation, and to be responsive to a second actuation of the keyboard to determine a measured value, indicative of the calibration value multiplied by the ratio of the extent to which the two reference indications are separated at the time of the second keyboard actuation to the extent to which the two reference indications are separated at the time of the first keyboard actuation. This measured value is indicated on a display on the measuring device. The measuring device disclosed in U.S. Pat. application Ser. No. 908,440, now abandoned, can be provided in a compact size, easily fitting within a pocket, and is capable of rapidly and accurately determining and indicating the value represented by an indication on a paper having a calibration scale and is suitable for numerous uses, including use by a doctor in evaluating an echocardiogram or other such indication of a patient's physical condition. Nevertheless, that measuring device is relatively costly to produce. The microprocessor is a comparatively expensive assembly, incorporating a central processing unit, a program memory, and a working memory. These components, as well as the keyboard, require a certain amount of space, limiting the compactness of the device.